1. Field of the Invention
This invention relates generally to locking rings for securing inner wellhead tubular members to outer wellhead tubular members. More particularly, this invention relates to a locking ring on an inner wellhead tubular member that is actuated by a series of pins that may be compressed by an annulus seal and that, when compressed, pushes the locking ring into engagement with the outer wellhead tubular member.
2. Brief Description of Related Art
Typically, locking mechanisms are used between inner and outer wellhead tubular members to help prevent relative axial movement between the members. In some cases, such locking mechanisms are integrated with seals or packoffs, which are typically used as a pressure barrier in the annular space between the inner and outer tubular members.
For example, U.S. Patent Appln. Pub. No. 2012/0025470 discloses an arrangement that includes a casing hanger inserted in a well bore. An annular seal is inserted so as to seal the space between the casing hanger and the well bore. To accomplish this, the annular seal includes ridges that, when pressed against surfaces of the casing hanger and the wellbore, become embedded in the surfaces. Not only does this arrangement seal the space between the casing hanger and the well bore, but it also locks the casing hanger in place axially relative to the wellbore.
One characteristic of such an integrated sealing/locking arrangement, is that ridges perform both a sealing and a locking function. Such an arrangement is advantageous in certain applications. It is possible, however, that there may be annulus seal designs that would perform the sealing function well, but that do not have the required profile to lock the casing hanger relative to the well bore. Another characteristic of such an integrated sealing/locking arrangement, is that the ridges, which lock the casing hanger in place by engaging the walls of the casing hanger and the well bore, are positioned in the load path for lockdown. Again, this feature is advantageous in certain applications. In some instances, however, it may be desirable to have a locking mechanism that is separate from the annulus seal, and not located in the load path. Such a situation may arise, for example, where there is a need to increase resistance to fatigue and the reliability of the seal.